Along with improvement of lifestyle and development of technology, besides electronic products having features of lightness, slimness, shortness and smallness, people have a great demand for electronic products having features of curling, easy to carry, comfortable touch feeling, low power consumption and easy maintenance, etc. However, the present semiconductors and electronic parts and components, etc. are all rigid materials, so that a product design thereof cannot satisfy the aforementioned demand. Therefore, flexible electronic parts and components technology is developed. A current variable-resistance array sensing device has advantages of easy usage, lightness and thinness, flexibility, irregular shape, drop proof, suitable for being fabricated through screen printing, suitable for customizing into different sizes and shapes, and simple structure, etc. Regardless of a single-point or an array type flexible variable-resistance pressure sensing device, in a macro perspective, equivalent circuits thereof are all variable resistors. However, a resistance value of the flexible pressure sensing device is varied along with a pressure variation, and a resistance variation range thereof is between several million ohms and several ohms. Regarding a conventional driving circuit, it is difficult to effectively readout a correct resistance value (a pressure value) of the flexible pressure sensing device from such large resistance variation range.
On the other hand, regarding a usage situation that the pressure is required to be monitored in long-term (for example, application products such as home medical care mattress/cushions, factory automation equipment, etc.), the conventional driving circuit may have a problem of large power loss due to that a pressure-resistance relationship curve of the pressure sensing device is a negative characteristic curve (i.e. the greater the pressure is, the smaller the resistance value is). A table 1 lists a relationship of resistance values and power loss of the pressure sensing device when different pressures are applied to the pressure sensing device. It is assumed that a bias voltage of the pressure sensing device is 3.3V. According to the table 1, it is known that when the flexible pressure sensing device is subjected to a smaller pressure (or no pressure), the resistance value of the pressure sensing device is about 1M ohm, and a power loss thereof P=I*I*R=0.00001089 W. When the flexible pressure sensing device is subjected to a medium pressure, the resistance value thereof is about 1000 ohm, and the power loss thereof P=0.01089 W (which is about 1000 times difference compared to the power loss without pressure). When the flexible pressure sensing device is subjected to a large pressure, the resistance value thereof is about 10 ohm, and the power loss thereof P=1.089 W (which is about 100000 times difference compared to the power loss without pressure).
TABLE 1relationship of pressure and resistance value of pressure sensing deviceResistance value ofPressuresensing device (Ω)Bias voltage (V)Power (W)Low pressure10000003.30.000010891000003.30.0001089100003.30.00108910003.30.010891003.30.1089High pressure103.31.089
When the flexible pressure sensing device is applied to a sleep quality mattress detection platform, to facilitate estimation, it is assumed that when a testee enters a deep sleep stage, the testee turns over the body once per hour. The pressure sensing device in the mattress are continuously subjected to a large pressure within the period of one hour. Regarding the pressure sensing device of the conventional driving circuit, the power loss of the pressure sensing device within the period of one hour probably exceeds 1 W. Therefore, during a sleep period of the testee, the pressure sensing device at least has power loss of 7-8 W.
Therefore, when the flexible pressure sensing device is applied to a system that requires to monitor pressure in long-term (for example, a home sleep quality monitoring system), the conventional driving circuit has unnecessary electric energy loss due to that the flexible pressure sensing device is in a large pressure environment for a long time.